Such valves are commonly used in slip-controlled hydraulic brake systems.
Valves for a slip-controlled hydraulic brake system are disclosed in German patent application P 37 01 019.0, each comprising a valve seat receiving a valve tappet, the valve tappet being moved by an electromagnet and being axially movably guided in a valve housing. An annular flow cross-section opens between the valve tappet and the valve seat when the valve tappet is shifted in a controllable manner, the flow cross-section communicating with pressure-fluid channels within the valve housing. To control all brake circuits, several valves are often included in a common valve block housing so that there is accomplished a space-saving positioning of each valve in an economical and cost-efficient manner.
What is to be considered less favorable in the known valve design is the noise behavior of the valve during the valve's shift periods, which behavior is due to the marginal layer separation of on the valve closure member circulated by hydraulic fluid as well as due to the resultant radial vibrations and/or the radial contact of the valve tappet on the valve seat in consequence of unstable flow.
In order to diminish the occurrence of noise and thus the transmission of sound conducted through the housing major passive and also active measures for noise attenuation are taken at present which, however, all entail considerable cost and offer more or less satisfying results.